UV-curable silicone compositions are well represented in the patent literature, and are assuming an increasingly significant share of various silicone coating applications. Such materials are curable by crosslinking reactions between radiation-sensitive functional groups such as acrylic or methacrylic functions attached to silicon atoms in the silicone polymer structure. However, silicones containing radiation-crosslinkable functional groups are not photo-curable unless a photosensitizer or photoinitiator is present in sufficient concentration to be effective.
A long-time problem for practitioners of this art has been the poor solubility of photosensitizers such as benzophenone, diethanolamine, and the like, in organofunctional dimethylsilicone polymers. One approach to this issue has been to produce silicone-functional photoinitiators which are designed to be miscible with silicone fluids.
Shirahata U.S. Pat. No. 4,391,963, teaches the synthesis of silicone-functional benzophenones. These materials are prepared by converting a hydroxybenzophenone to an allyloxy benzophenone, then adding the unsaturated benzophenone derivative to an SiH containing polysiloxane via platinum-catalyzed addition. This scheme is complex and requires conversion of a hydroxybenzophenone (or hydroxyacetophenone) to another intermediate, followed by a hydrosilation reaction. Further, there is a problem that the hydrosilation reaction prevents the simultaneous substitution to the polysiloxane of unsaturated hydrocarbon functions as such functions will be consumed in the reaction. There are other such examples which can be culled from prior art.
It is an object of the present invention to produce a silicone polymer which is self-sensitized to UV radiation.
It is another object of the present invention to produce a polymer having both radiation sensitive acrylic or methacrylic functional and photosensitizing organo-functionality.
It is yet another object to produce such a polymer via one-pot processing by means of well known synthesis techniques.
It is still another object to produce such a polymer without need for hydrosilation reactions.